Do you know the difference between a dependent event and an independent event? If someone runs a 5 minute mile and someone else runs a 10 minute mile are these two events dependent on each other?
In this concept, you will learn to recognize independent events and dependent events.
Independent and Dependent Events
When you work with probability, you can think about different events and how these events impact each other. Let’s look at an example.
Suppose there are two events:
The probability of each of these events by itself is easy enough to compute. In general:
If this is the case, then you can write the following ratios for rolling a 5 and spinning blue.
If the outcome of one event has no effect on the outcome of a second event, then the two events are independent events.
Now let’s think about a different kind of example, one where the outcome of one event does impact the outcome of another event.
A bag has 3 red marbles, 4 blue marbles, and 3 green marbles. Irene pulls 1 green marble out of the bag. Does this change the probability that the next marble Irene pulls out of the bag will be green?
First, find the number of favorable outcomes and the total number of outcomes for the first pick from the bag.
Next, find the probability of choosing a green marble.
Then, for the second marble, there are now only 9 marbles left in the bag and only 2 of them are green. So the probability of pulling out a green marble for the second marble is now:
Clearly, the first event affected the outcome of the second event in this situation. So the two events are NOT independent. In other words, they are dependent events.
If the outcome of one event has an effect on the outcome of a second event, then the two events are dependent events.
To calculate the probability of overlapping events, list the sample space and find the favorable events.
The probability of red-top is:
Earlier, you were given a problem about the race and the two runners. Two runners are in a race. The first runner runs a 5 minute mile and the second runner runs a 10 minute mile.
The events are independent. The speed of one runner does not impact the speed of another runner.
First, identify the overlapping outcomes of both events.
Next, find the total number of outcomes.
Then, find the probability of the overlapping events.
Identify whether the following events are independent or dependent.
Rolling a 1 and then rolling a 6 on a number cube.
The answer is these events are independent events because the rolling of a one does not affect the second roll and getting a six.
A bag has a red and two blue marbles.
First, one blue marble is drawn and then replaced.
Then, a red one is drawn.
Are these two events dependent or independent?
The answer is these events are independent events because the blue marble was replaced; it does not affect the outcome of drawing of red.
A box contains 5 white and 6 red marbles. What is the probability of successfully drawing, in order, a red marble and then a white marble?
The answer is these events are dependent events because the red marble was not replaced; the number of total outcomes will decrease from 11 to 10 when choosing the white marble.
Write whether events A and Bare dependent or independent.
1. A: Doug flips a coin. B : Marlene chooses a card out of a deck.
2. A: In a bag with 5 white marbles and 5 black marbles, Sanjay pulls out a white marble. B : Without returning the marble to the bag, Sanjay pulls out a second marble.
3. A: Eddie chooses the color blue for his new bike. B : Eddie chooses lasagne from the dinner menu.
4. A: The probability that it will rain tomorrow. B : The probability that the Red Wings hockey team will win their game tomorrow.
5. A: The probability that it will rain tomorrow. B: The probability that the baseball team will have a rain delay.
6. A: From a deck of cards, the probability of one player drawing a heart from the deck. B : On the next player’s turn, the probability of drawing another heart.
7. A: The probability of a spinner landing on blue 6 times in a row. B : The probability of the spinner landing on blue on the next spin.
8. A: The probability of flipping a coin and having it come up heads. B : The probability of flipping it again and having it come up heads.
9. A: The probability that it will snow tomorrow. B : The probability of having a snow day from school.
10. A: The probability that it will be 90 degrees. B : The probability of enjoying a hot day at the beach.
11. A: The probability that it will rain tomorrow. B : The probability of getting an A on a math test.
12. A: The probability that the Rockies will be in the playoffs. B: The probability that the Rockies will win the World Series.
13. A: The probability that tomorrow will be sunny. B : The probability that tomorrow will be a full moon.
14. A: The probability that tomorrow will be sunny. B : The probability that tomorrow will be cloudy.
15. A: The probability that it will cold today. B : The probability that it will be a full moon tomorrow.
To see the Review answers, open this PDF file and look for section 11.12.